Green with envy? How human faces really do change colour with emotion

This composite image shows a happy face as it was originally photographed (left) and the same photo retouched to emphasize changes in color. 
This composite image shows a happy face as it was originally photographed (left) and the same photo retouched to emphasize changes in color.  Credit: Ohio State University 

Whether it is arguing until ‘blue in the face’ or feeling ‘green with envy’ the English language is well-stocked with idioms linking colour to emotion.

Now for the first time, scientists have shown that people actually do change hue depending on their feelings.

Although it is a subtle alteration to skin tone and complexion around the nose, eyebrows, cheeks or chin, the effects are picked up subconsciously by observers, making it very hard to hide emotions.

It means that a sad person, attempting to put on a brave face will still flush the colour of his or her unhappiness, inadvertently showing the turmoil behind their smile.

The scientists believe the changes of colour are triggered by blood flow channelled from the central nervous system to  depending on our state of mind.

"We identified patterns of facial coloring that are unique to every emotion we studied," said Dr Aleix Martinez, cognitive scientist and professor of electrical and computer engineering at Ohio State University.

"We believe these color patterns are due to subtle changes in blood flow or blood composition triggered by the central nervous system.

“Not only do we perceive these changes in facial color, but we use them to correctly identify how other people are feeling, whether we do it consciously or not."

An original and enhanced 'angry' face

For the study, the researchers first took hundreds of pictures of facial expressions and separated the images into different color channels that correspond to how human eyes see colour - either in a red/green channel or blue/yellow.

They then ran the images through computer analysis and found that emotions such as ‘happy’, ‘sad’, ‘anger’ or ‘disgust’ all formed unique color patterns.

‘Disgust’, for instance, creates a blue-yellow cast around the lips, but with a red-green cast around the nose and forehead.

Happiness is seen in red at the checks and temples and a little blue around the chin, but the same face with a slightly redder forehead and slightly less blue chin registers as ‘surprised.’

Although the team did not look at 'envy' they suggest that the green colour linked to feelings of jealousy could stem from the nausea which often accompanies the emotion. 

An original and enhanced 'happy' face

To test whether colors alone could convey emotions - without smiles or frowns to go along with them - the researchers then superimposed the different emotional color patterns on pictures of faces with neutral expressions.

They found that volunteers were able to spot an emotion up to 75 per cent of the time. The effect remained regardless of gender, ethnicity or overall skin tone.

Next, researchers showed participants facial expressions of happiness, sadness and other emotions but mixed up the colors of the the images, for example putting ah angry hue on a happy face. Participants reported that something was ‘off’ but could not put their finger on what was wrong.

"Participants could clearly identify which images had the congruent versus the incongruent colors," added Prof Martinez.

"People have always said that we use makeup to look beautiful or younger, but I think that it is possible that we actually do it to appear happier or create a positive perception of emotion--or a negative perception, if you wanted to do that.”

It also enabled researchers to construct computer algorithms that correctly recognize human emotion via face color up to 90 percent of the time.

Happiness was the easiest emotion for the computer to recognize by color alone, and it detected the emotion with 90 percent accuracy. Anger was detectable by color alone 80 percent of the time, and sadness 75 percent of the time. Fear was recognizable 70 percent of the time.
